1. Field of the Invention
The present invention relates to a signal relay device and method thereof, and in particular to a system using the signal relay device, relaying an SS7 (Signaling System 7) signal from a PSTN (public switched telephone network) to an IP (Internet protocol) network.
2. Description of the Related Art
Conventional PSTNs, used in analog stations and fax transmission, and IP networks, used in digital data transmission, function under different networking protocols. For development of digital signal processing (DSP) and computer telephone integration (CTI) technologies, modern products and services extend new applications in computers and telephones like computer telephone application generators, unified message systems (UMS), and automatic call distribution, integrating them with Internet function to provide Internet telephone gateways.
Voice over Internet protocol (VoIP), based on international telecommunication union-telecommunication standardization sector (ITU-T) H.323, provides basic call services. The H.323 architecture, however, cannot equip current VoIP systems for future integration with PSTN. Signals for a PSTN call are passed via a trunk gateway and SS7 signals network. SS7-ISUP (Integrated Service Digital Network User Part) signaling takes charge of the call, passing between an originating switch and a terminal switch through signal transfer points of an SS7 network for general communication. In an Internet telecommunication architecture, an IP network works with a conventional telecommunication network through an SS7 network and signal gateway (SG), receiving signals from the SS7 network, which is then converted and transferred to a media gateway controller (MGC), capable of call control and routing, signaling processing, media gateway control, and call detail recording (CDR).
In a conventional PSTN, signaling is transferred through signal transfer points to a local exchange to be marked and then transmitted to a telephone receiver. In addition, signaling is transferred among signal transfer points according to routing tables internally established, wherein the signal transfer points pick an available route to determine a new transfer point when a subsequent transfer point is unavailable. A signal gateway is a bridge between an SS7 network and an IP network, transferring call control messages as ISUP signaling. The single channel between a signal gateway and a media gateway controller, however, cannot bridge an SS7 network and an IP network.
In U.S. patent application Pub. No. 2002/0027983, Suzuki et al disclose a gateway system having a redundant structure of media gateway controllers, relating to a gateway system utilizing a common channel signaling system to connect an existing telephone network to an IP network, enhancing reliability without system downtime even during failure. The gateway system comprises a media gateway and a controller group therefor, comprising a plurality of media gateway controllers assigned with a common point code. Any of the media gateway controllers can terminate an SS7 signal representative of a control signal of the common channel SS7 in the telephone network and carry out call and connection control to the IP network by controlling the media gateway through the IP network. Thus, a communication path is established between the telephone network and the media gateway. Drawbacks of the application include the combination of signal gateways and media gateway controllers being unusual and lacking flexibility for receiving signals and synchronization data traffic between media gateway controllers is heavier due to synchronization signals from other media gateway controllers